1. Field of the Invention
The present invention relates to a turntable-type acceleration generating apparatus (rotary-type acceleration generating apparatus) which is suitable for examining characteristics of an acceleration sensor for sensing an acceleration. More particularly, the present invention relates to an eccentric error corrector for correcting an eccentric error of an acceleration sensor in a rotary acceleration generating apparatus, which the device can readily correct eccentricity between the center of gravity on the sensing axis of the acceleration sensor and the rotational center of the small-diameter turntable when an acceleration sensor is placed on a small-diameter turntable (small-diameter rotary member) in examining the sensor characteristics, and can simply and exactly measure the characteristics of the acceleration sensor regardless of quantity of the eccentricity, and a method of removing an eccentric error of an acceleration sensor in the rotary acceleration generating apparatus.
2. Description of the Related Art
Acceleration of an object moving in a three-dimensional space, e.g., robots and air planes, and another object moving in two-dimensional space, e.g., motor vehicles, are sensed by an acceleration sensor. Motions of the object or various devices installed on the object are controlled in accordance with the thus gathered data for intended purposes. Various types of acceleration sensors are currently used for this type of control. Therefore, it is necessary to know the characteristics of the acceleration sensors before the sensors are assembled into the control devices.
A vibration tester is currently used for examining the characteristics of the acceleration sensor. However, the examining method using the vibration tester has the following problems.
(1) The vibration tester examines an acceleration characteristic of an object to be examined in a manner that the object is located on a testing table and subjected to a reciprocative acceleration. Sometimes, the testing table somewhat slants during the reciprocative operation (vertical vibration) of the testing table. The table slanting makes it difficult to secure an exact reciprocative motion. Where the table slants, a force component is additionally applied to the acceleration sensor under test in the directions different from those of the reciprocative forces. The resultant of the measurement includes an interference component in addition to an acceleration of the sensor. The interference component contained in the measurement result impairs the examination of the characteristics of the acceleration sensor in examination exactness.
(2) In the above-mentioned vibration tester, the acceleration sensor is actually vibrated by a vibration generator. Therefore, the tester per se is inevitably large in scale. Further, it is necessary to actually apply a dynamic acceleration of the vibration to the acceleration sensor. This results in complexity of the testing procedure.
For this background, the inventors of the present Patent Application proposed the solution to the problems. The solution takes the form of a novel centrifugal acceleration tester (turntable-type acceleration generating apparatus) capable of remarkably improving the testing accuracy (Japanese Unexamined Patent Publication No. Hei. 7-110342). In the tester, an acceleration sensor is placed on a testing table, and a predetermined acceleration (i.e., a DC component of acceleration) is applied to it in a predetermined direction, whereby the characteristics of the acceleration sensor are examined with high precision.
In examining the characteristics of the acceleration sensor by use of the turntable acceleration generating apparatus, it is almost impossible, in practical use, to make the center of gravity on the sensitivity axis of the acceleration sensor as an object to be examined coincident with the rotational center of the small-diameter turntable. Accordingly, an eccentricity between the center of gravity on the sensitivity axis of the acceleration sensor and the rotational center of the small-diameter turntable inevitably gives rise to an error in an output signal of the acceleration sensor. Therefore, the error contained in output signal must be corrected with a various method.
In examining the characteristics of the commercially available acceleration sensor, it is very important to know the center of gravity on the sensitivity axis of the acceleration sensor. So far, there is no technique to exactly know the center of gravity on the sensitivity axis. For this reason, the characteristic output value of the acceleration sensor inevitably contains an error which is caused by the eccentricity of the center of gravity on the sensitivity axis, so that one cannot exactly know the characteristics of the acceleration sensor. The testing of the characteristic test of the acceleration sensor by use of the turntable-type acceleration generating apparatus is considerably easier than the testing which uses the conventional vibration type acceleration tester. However, the center of gravity on the sensitivity axis of the acceleration sensor accurately cannot be certainly made coincident with the rotational center of the small-diameter turntable. Thus, the conventional sensor characteristic testing is unsatisfactory in precisely knowing the characteristics of the acceleration sensor.
For the above-mentioned background, the inventor of the present Patent Application concentrated his energy on developing a technical method for removing the adverse effect by the eccentricity of the center of gravity on the sensitivity axis of the acceleration sensor. Through the study, it was found that a low frequency component indicating the characteristics proper to the acceleration sensor and a DC component (eccentric error component) which is caused by an eccentricity of the center of gravity on the sensitivity axis are contained in a superimposing fashion in the output signal that is output from the acceleration sensor when it is operated by use of the turntable-type acceleration generating apparatus.
The present invention has been made on the basis of the above-mentioned finding, and proposes an eccentric error corrector and method for correcting an eccentric error of the center of gravity on the sensitivity axis of an acceleration sensor set in a turntable-type acceleration generating apparatus. The eccentric error corrector is capable of correcting an eccentric error by removing the DC component even if the center of gravity on the sensitivity axis of an acceleration sensor is located at any eccentric position relative to the rotational center of a small-diameter turntable. Accordingly, this is an object of the present invention to solve the above-mentioned problems.
According to the present invention, even if the center of gravity on the sensitivity axis of an acceleration sensor is located at any eccentric position or at unknown position, one can proof the acceleration sensor and always know the exact characteristic of the acceleration sensor.
To solve the above problems, there is provided an eccentric error corrector for removing the effect by an eccentric error of an acceleration sensor, which the device is used in combination with a rotary acceleration generating apparatus having a large-diameter turntable rotated by a first servo motor and a small-diameter turntable which is mounted on an appropriate location on the outer periphery portion of the large-diameter turntable while being rotatable by a second servo motor, and allows an acceleration sensor to be attached thereto. The eccentric error corrector includes a DC-component remover which removes only the DC component from an output signal of an acceleration sensor placed on the small-diameter turntable.
In the eccentric error corrector, the DC component remover may be a high-pass filter.
The present invention also provides a method for removing the effect by an eccentric error of an acceleration sensor, which the method is used for a rotary acceleration generating apparatus having a large-diameter turntable rotated by a first servo motor and a small-diameter turntable which is mounted on an appropriate location on the outer periphery portion of the large-diameter turntable while being rotatable by a second servo motor, and allows an acceleration sensor to be attached thereto. The method includes the steps of: placing an acceleration sensor as an object to be inspected on the small-diameter turntable; and removing a low frequency component from an output signal of the acceleration sensor placed on the small-diameter turntable when the large- and small-diameter turntables are rotated, to thereby remove an error caused by an eccentricity of the center of gravity on the sensitivity axis of the acceleration sensor with respect to the rotational center of the small-diameter turntable.